Add integration tests for storage credential refreshers #15
Description
Each major object storage platform has its credentials refresher:
org.apache.iceberg.aws.s3.VendedCredentialsProviderorg.apache.iceberg.gcp.gcs.OAuth2RefreshCredentialsHandlerorg.apache.iceberg.azure.adlsv2.VendedAdlsCredentialProvider
All of them have internal AuthManagers because they need to contact the REST catalog. Therefore, we should have integration tests that exercise them.